25 research outputs found
Achieving One‐Step Surface Coating of Highly Hydrophilic Poly(Carboxybetaine Methacrylate) Polymers on Hydrophobic and Hydrophilic Surfaces
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108623/1/admi201400071.pd
Biologically Inspired Stealth Peptide-Capped Gold Nanoparticles
Introduction into the human body
makes most nanoparticle systems
susceptible to aggregation via nonspecific protein binding. Here,
we developed a peptide-capped gold nanoparticle platform that withstands
aggregation in undiluted human serum at 37 °C for 24 h. This
biocompatible and natural system is based on mimicking human proteins
which are enriched in negatively charged glutamic acid and positively
charged lysine residues on their surface. The multifunctional EKEKEKE-PPPPC-Am
peptide sequence consists of a stealth glutamic acid/lysine portion
combined with a surface anchoring linker containing four prolines
and a cysteine. Particle stability was measured via optical spectroscopy
and dynamic light scattering in single protein, high salt, and undiluted
human serum solutions. In vitro cell experiments demonstrate EKEKEKE-PPPPC-Am
capped gold nanoparticles effectively minimize nonspecific cell uptake
by nonphagocytic bovine aortic endothelial cells and phagocytic murine
macrophage RAW 264.7 cells. Cytotoxicity studies show that peptide-capped
gold nanoparticles do not affect cell viability. Finally, the peptide
EKEKEKE-PPPPC-Am was extended with cyclic RGD to demonstrate specific
cell targeting and stealth without using poly(ethylene glycol). Adding
the functional peptide via peptide sequence extension avoids complex
conjugation chemistries that are used for connection to synthetic
materials. Inductively coupled plasma mass spectroscopy results indicate
high aortic bovine endothelial cell uptake of c[RGDfE(SGG-KEKEKE-PPPPC-Am)]
capped gold nanoparticles and low uptake of the control scrambled
sequence c[RDGfE(SGG-KEKEKE-PPPPC-Am)] capped gold nanoparticles
Sequence, Structure, and Function of Peptide Self-Assembled Monolayers
Cysteine is commonly used to attach peptides onto gold
surfaces.
Here we show that the inclusion of an additional linker with a length
of four residues (-PPPPC) and a rigid, hydrophobic nature is a better
choice for forming peptide self-assembled monolayers (SAMs) with a
well-ordered structure and high surface density. We compared the structure
and function of the nonfouling peptide EKEKEKE-PPPPC-Am with EKEKEKE-C-Am.
Circular dichroism, attenuated total internal reflection Fourier transform
IR spectroscopy, and molecular dynamics results showed that EKEKEKE-PPPPC-Am
forms a secondary structure while EKEKEKE-C-Am has a random structure.
Surface plasmon resonance sensor results showed that protein adsorption
on EKEKEKE-PPPPC-Am/gold is very low with small variation while protein
adsorption on EKEKEKE-C-Am/gold is high with large variation. X-ray
photoelectron spectroscopy results showed that both peptides have
strong gold–thiol binding with the gold surface, indicating
that their difference in protein adsorption is due to their assembled
structures. Further experimental and simulation studies were performed
to show that -PPPPC is a better linker than -PC, -PPC, and -PPPC.
Finally, we extended EKEKEKE-PPPPC-Am with the cell-binding sequence
RGD and demonstrated control over specific versus nonspecific cell
adhesion without using poly(ethylene glycol). Adding a functional
peptide to the nonfouling EK sequence avoids complex chemistries that
are used for its connection to synthetic materials
Standardizing and Simplifying Analysis of Peptide Library Data
Peptide libraries allow researchers to quickly find hundreds
of
peptide sequences with a desired property. Currently, the large amount
of data generated from peptide libraries is analyzed by hand, where
researchers search for repeating patterns in the peptide sequences.
Such patterns are called motifs. In this work, we describe a set of
algorithms which allow quick, efficient, and standard analysis of
peptide libraries. Four main techniques are described: (1) choice
of the number of motifs present in a peptide library; (2) separation
of the peptides into groups of similar sequences; (3) fitting of a
model to the peptides to extract motifs; (4) analysis of the library
using quantitative structure–property relationships if no clear
motifs are present. The application of five previously published data
sets shows these techniques can automatically repeat the work of experts
quickly and allow much more flexibility in analysis. A new way of
visually presenting peptide libraries is also described, which allows
visual inspection of the grouping and spread of sequences. The algorithms
have been implemented in an open-source plug-in called “peplib”
and an online web application
Free Energy of Solvated Salt Bridges: A Simulation and Experimental Study
Charged
amino acids are the most common on surfaces of proteins
and understanding the interactions between these charged amino acids,
salt bridging, is crucial for understanding protein–protein
interactions. Previous simulations have been limited to implicit solvent
or fixed binding geometry due to the sampling required for converged
free energies. Using well-tempered metadynamics, we have calculated
salt bridge free energy surfaces in water and confirmed the results
with NMR experiments. The simulations give binding free energies,
quantitative ranking of salt bridging strength, and insights into
the hydration of the salt bridges. The arginine–aspartate salt
bridge was found to be the weakest and arginine-glutamate the strongest,
showing that arginine can discriminate between aspartate and glutamate,
whereas the salt bridges with lysine are indistinguishable in their
free energy. The salt bridging hydration is found to be complementary
to salt bridge orientation with arginine having specific orientations
Sensitive and Fast Detection of Fructose in Complex Media via Symmetry Breaking and Signal Amplification Using Surface-Enhanced Raman Spectroscopy
A new
strategy is proposed to sensitively and rapidly detect analytes
with weak Raman signals in complex media using surface-enhanced Raman
spectroscopy (SERS) via detecting the SERS signal changes of the immobilized
probe molecules on SERS-active substrates upon binding of the analytes.
In this work, 4-mercaptophenylboronic acid (4-MPBA) was selected as
the probe molecule which was immobilized on the gold surface of a
quasi-three-dimensional plasmonic nanostructure array (Q3D-PNA) SERS
substrate to detect fructose. The molecule of 4-MPBA possesses three
key functions: molecule recognition and reversible binding of the
analyte via the boronic acid group, amplification of SERS signals
by the phenyl group and thus shielding of the background noise of
complex media, and immobilization on the surface of SERS-active substrates
via the thiol group. Most importantly, the symmetry breaking of the
4-MPBA molecule upon fructose binding leads to the change of area
ratio between totally symmetric 8a ring mode and nontotally symmetric
8b ring mode, which enables the detection. The detection curves were
obtained in phosphate-buffered saline (PBS) and in undiluted artificial
urine at clinically relevant concentrations, and the limit of detection
of 0.05 mM was achieved
One-Step Dip Coating of Zwitterionic Sulfobetaine Polymers on Hydrophobic and Hydrophilic Surfaces
Zwitterionic sulfobetaine polymers
with a catechol chain end (DOPA-PSB) were applied to a variety of
hydrophobic polymer sheets and fibers. In addition, a silica surface
was tested as a representative hydrophilic substrate. The polymer-coated
surfaces showed significantly lower fouling levels than uncoated controls.
Because of the anti-polyelectrolyte nature of sulfobetaine zwitterionic
polymers, the effect of salt concentration on the coating solutions
and the quality of the polymer coating against fouling are studied.
The coating method involves only water-based solutions, which is compatible
with most surfaces and is environmentally friendly. To demonstrate
the versatility of the reported method, we evaluated the fouling levels
of the polymer coating on commonly used polymeric surfaces such as
polypropylene (PP), polydimethylsiloxane (PDMS), polystyrene (PS),
nylon, polyvinyl chloride (PVC), and poly(methyl methacrylate) (PMMA)